THE SERVICE OF TAILS 



79 



against the wall of a hollow tree, rock-crevice, or 

 chimney. As a result, the end of the tail-feathers 

 of such birds has become stiffened and capable of 

 this special work to a remarkable degree ; while in 

 the case of the common chimney swift, and some 

 similar, rock-climbing species of 

 the East, the shafts of the 

 feathers project beyond the 

 vanes in long, sharp spines, 

 equal in effect to the climbing- 

 irons of a telegraph lineman. 



Among animals that live in 

 the water, the tail becomes of 

 supreme importance in loco- 

 motion. The shrimp's swim- 

 ming is wholly by reaching its 

 tail out and pulling itself back- 

 ward. This, of course, is the principle of the oar ; 

 and the shrimp is able to "feather," since the 

 plates of his tail shut up like a fan in recovering 

 for a new stroke. 



It is mainly as a screw-propeller, however, that 

 their tails serve the swimmers — precisely the mo- 

 tion a man makes when sculling a boat by a single 

 oar held over the stern. This motion is plainly 

 visible in fishes, the most swift and powerful among 

 which have the smallest body-fins ; and it is solely 

 by this sculling movement of the tail that the shark 

 and bluefish make such terrific rushes after prey, 

 that the trout is able to give the angler so much 



Spines terminating 

 THE Tail-quills 

 OF A Swift. 



